Hum. Interesting except in many other days, weeks, months my cam has recorded miles of video. So, is your comment based on something new?
No, what I describe is how the system has always worked (and it's exactly how it's explained in the owners manual) with only the exception that until pretty recently it wouldn't auto-delete old sentry files if the drive filled up (instead it'd just change the red camera icon to a grey x and stop recording until you clearly space off yourself) and they changed the folder naming a bit... see below on that.
Are the videos of the car moving or parked?
Sentry records when you are parked. DashCam records when you are moving.
Nope.
Sentry records never.
Dash cam is always what is recording.
If the car is on (powered on- if you're driving or not makes no difference) than dash cam is recording- unless you manually turn it off or don't have an appropriate USB storage device attached. Sentry, when activated, keeps the car "on" so he dash cam keeps recording.
On the key there's 3 folders.
Recent is the last 60 minutes of footage. Always. It overwrites itself as needed.
Saved is where the last 10 minutes from anytime you tap the camera icon to "save" footage goes.
Sentry is where sentry mode moves the last 10 minutes any time it goes to alert mode. That's all sentry is doing, video-wise... moving the DASH CAM last 10 minutes from Recent into the sentry folder to keep it from being auto-overwritten 60 minutes later.
This is also why you can't turn on dash cam with no USB storage, but you CAN turn on sentry- it'll still do everything else (warning on the screen and flash the lights when someone comes near to put it into alert- blare the stereo with classical music for an alarm, etc) it just won't move the video since it doesn't exist without dash cam running.
The folder change they made a couple updates ago was there used to be just a saved folder where what now goes into saved AND sentry used to both go... they separated em to make it a bit clearer which was which.
Also, AFAIK, the car will self-delete the oldest files in Sentry if it's running out of space...but won't ever delete the files in Saved.